Significant Increase in Human Activities Since 1850 According to Multiple Proxies of Sihailongwan Maar Lake Sediment

Based on a global comparison of geological records, the International Anthropocene Working Group (AWG) determined that the onset of the Anthropocene was sometime in the mid-twentieth century (~1950 CE), and the Sihailongwan Maar Lake has been included as one of the candidate sites for the Global boundary Stratotype Section and Point (GSSP) of the Anthropocene. However, humans had a profound impact on the environment of the areas around Sihailongwan Maar Lake even before 1950 CE. Historical sequences of TOC contents, C/N ratios, δ¹³C_org values, Ca/Ti ratios, and concentrations of silicate major elements, such as Si, Al, and K, since 900 CE were reconstructed, with the average resolution being ~10 a, to explore the history of human activities in this region under the background of climate change. Human activities have significantly increased since 1850 CE, and changes in the measured proxies during the Medieval Warm Period and Little Ice Age before 1850 CE generally follow natural laws. The changes in the measured proxies during 1850-1950 CE indicate a rapid population growth, which damaged vegetation and resulted in intensified weathering and deviation of the surface environment evolution from the natural state. Hence, humans had started to be an important force for the geological environment; nevertheless, the changes during this period resulted in mostly local signals. After 1950 CE, the C/N ratios and δ¹³C_org values decreased continuously, indicating that the environmental status of the area around Sihailongwan Maar Lake changed once again under the new government and advanced productivity. This was in sync with the Great Acceleration of the global geological environment and supports the conclusion of the AWG that the onset of the Anthropocene was sometime in the mid-twentieth century.